The invention relates to a method for processing film images deviated from a film recording optical path of a moving picture camera and to a device for implementing the method.
From U.S. Pat. No. 4,928,171 a video device is known for a moving picture camera in which a video image sensor is mounted in an optical path of the moving picture camera which is periodically interrupted according to the image-recording frequency of the moving picture camera. A video device of this kind serves to produce parallel to the exposure of film images of the moving picture film a video image which on the one hand during film recording enables the picture to be viewed independently of looking into the camera viewfinder and on the other hand makes it easier to refinish the exposed moving picture film using recorded video sequences.
For this purpose a part of the recording optical path of the moving picture camera is divided off into a video path and directed to a video image sensor or video camera. The recording lens of the moving picture camera thereby projects an image in the image plane of the moving picture film which is moved intermittently for example with a film transport speed of 24 images per second when a rotatable mirror aperture mounted in the recording beam path of the moving picture camera behind the recording lens releases the recording beam path during exposure of a film image. In the time in which the moving picture film is moved further by a film image division the movable mirror aperture covers the recording path to the image plane and diverts the film image onto the plane of a matt disc or fibre plate from where the ensuing image is copied via a video optic to a video image sensor.
The video image sensor integrates the light of the video beam path falling on its light-sensitive layer. The integrated signals are periodically picked out from the video image sensor and displayed as video output signals on a video monitor or are stored on a suitable storage medium.
Between the matt disc or fibre plate and the video optic is at least one further beam divider which diverts the image of the matt disc or fibre plate to an eyepiece through which a cameraman can view the film image on the matt disc.
As a result of the periodic interruption of the recording path of the moving picture camera according to the image recording frequency of the moving picture camera, no light passes onto the video image sensor during the film exposure which-apart from special cases-leads to image flickering of the video image which can be generated with the video output signal of the video image sensor. This flickering of the image is intensified if the time active for loading an image point of the loading image of the video image sensor between the last unloading reading and the next unloading reading of the loading image of the video image sensor is shortened through time intervals which change from image to image during which the video path to the video image sensor is interrupted.
The relevant time span of the active exposure for an image point of the loading image of the video image sensor between an unloading reading of the loading image to generate the video output signal and the next unloading reading of the loading image for generating the next video output signal is thereby a different length from image to image since the usual image recording frequency of a moving picture camera only agrees with the video frequency of the video device in exceptional cases. Thus for example the picture recording frequency of a moving picture camera normally amounts to 24 images per second, whilst the video frequency of a video device with a PAL system amounts to 50 images per second and with an NTSC system to 60 images per second. This image flickering results in a light/dark change of a video image or video semi image which makes viewing the video image difficult or even impossible.
In order to eliminate or reduce this image flickering it is known from U.S. Pat. No. 4,928,171 to control the video image sensor light-sensitive only when light is available in the video beam path. The video image sensor is thereby coupled to the moving picture camera in respect of the video frequency and phase position. In order to obtain from this again standard video signals with 25 (PAL system) or 30 images per second (NTSC system) the video signals of the video image sensor or the video camera connected thereto are stored interim in the frequency of the video image sensor and are retrieved from the intermediate store in the standard video signal frequency.
Thus, independently of the film transport speed or image recording frequency of the moving picture camera, the video output signal of the known video device corresponds to the standard video image frequency and is provided at the output of the video device in the form of a FBAS (Farbart Bildanteil Abtast-und Synchronisations) signal (colour type, image content, scanning and synchronising signal) for display on a video monitor or for video signal storage.
A significant drawback of this rigid video assist system is that through the generation and issue of standard video images it is not possible to deal with special features of a moving picture film. This leads to problems when touching up or finishing the moving picture film and to dispensing with special effects which can be produced with the moving picture film but which cannot be displayed with the video device for the following reasons.
Since the standard image recording frequency of a moving picture camera amounts to 24 images, for refinishing a moving picture film and more particularly for film cutting, cutting computers are already known which operate with a time resolution of 24 images per second so that when using a video recording for facilitating the refinishing of the moving picture film first it is necessary to convert the video signal in dependence on the relevant system (PAL or NTSC) with a video frequency of 25 or 30 video images per second to the image recording frequency of the moving picture camera of 24 images per second.
Furthermore the rigid standard video image frequency does not allow the reproduction of slow motion or quick motion effects of a moving picture film which was exposed with an image recording frequency deviating from the standard image recording frequency. The moving picture camera for generating a slow motion effect is moved with a higher transport speed or for generating a time-lapse effect is moved with a lower film transport speed than the standard film transport speed of image recording frequency. If the moving picture film is moved on projection again with the normal standard image recording frequency of 24 images per second then the corresponding slow motion and quick motion effects are produced. These effects can only be displayed inadequately owing to the rigid standard video image frequency.
There are indeed methods known for electronically completing these effects but all set-ups have lead to an unclear, jolting motion resolution.
Furthermore the fact that light is available in the viewfinder and thus on the video sensor for only half a complete film image cycle is the cause of a half image resolution in the video output signal. Normally an odd or even half image is always correctly exposed and the other half image is exposed at the time when the sensor does not receive any light. In order however to obtain a video picture which does not even show the disruptive light/dark sequences the contents of the unexposed half images is replaced by the content of the previously exposed half images. The information which would exist with a non-interrupted exposure in the second half image is thereby automatically lost.